1. Field of the Invention
The present invention relates to an internal pressure container and its manufacturing method.
2. Related Art
An internal pressure container in which a fiber reinforced resin made sleeve 20 produced by winding a continuous fiber by a filament winding method is closed at both ends by closure lids 21 and the closure lids 21 are supported by retainer rings 22 coupled with the sleeve 20 is used in, for example, a seawater purifying apparatus as shown in FIG. 1. An end portion B of the above-described sleeve 20 is large in diameter in comparison with the other end portion A thereof.
The reason why the above-described sleeve 20 has such a configuration, it may receive well an internal pressure applied to the closure lid 21 of the end portion B of the sleeve 20 and the retainer ring 22 thereof. (Since the retainer ring 22 is embedded in the sleeve 20, the thickness of the end portion B is increased.)
More specifically, in order to give a desired thickness to a portion to become the end portion B of the above-described sleeve 20 by winding a fiber around a mandrel, the above-described fiber is continuously wound by a hoop winding substantially at 90 degrees to an axis of the mandrel. Thereafter, the above-described fiber is continuously wound over the entire range of the mandrel substantially at a uniform thickness by a helical winding substantially at 55 degrees to the axis of the mandrel. Incidentally, a desired mechanical strength may be attained by the helical winding.
However, in the case where the above-described sleeve 20 is formed as described above, an interface between a layer X wound and laminated by the above-described hoop winding and a layer Y wound and laminated by the above-described helical winding is in parallel with an axial load due to the inner pressure in cross-section as shown in FIG. 2. When the internal pressure is applied thereto, a peel occurs between the layers. Thus, there is a problem that the closure lid 21 falls away.
In a durable internal mechanical strength is set at 400 kg/cm2 or more, such a problem may be solved, for example, by setting the thickness of the end portion B of the sleeve 20 (in general, 40 mm or more) or setting a distance from the closure lid 21 to the end portion B (in general, 150 mm or more). However, these countermeasures lead to a large-size problem or a high cost problem disadvantageously.
In particular, if the thickness of the end portion is more than 40 mm, an interval between a plurality of internal pressure containers to be juxtaposed with each other in forming the seawater purifying apparatus is increased, so that the size of the apparatus is enlarged. On the other hand, if the length from the end portion to the retainer ring exceeds 150 mm, mounting and dismounting of bolts would be troublesome when the retainer rings are removed for mounting a reverse permeation membrane that is needed to the seawater purifying apparatus.
Also, it is proposed to make a structure in which an inner ring to receive the internal pressure applied to the retainer ring. However, in this case, the inner ring has to be installed internally and at the same time, an integral molding has to be performed. Accordingly, the filament winding must be done to be in compliance with such complicated steps.